Polishing apparatus and polishing method

ABSTRACT

A polishing apparatus for polishing a periphery of a substrate includes a substrate holder configured to rotate the substrate, a first polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a first polishing tool into contact with the periphery of the substrate when rotated by the substrate holder, and a second polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a second polishing tool into contact with the periphery of the substrate when rotated by the substrate holder. The polishing layer of the first polishing tool has hard first abrasive grains, and the polishing layer of the second polishing tool has second abrasive grains that are softer than the first abrasive grains.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing apparatus and a polishing method for polishing a substrate, such as a semiconductor wafer, and more particularly to a polishing apparatus suitable for use as a bevel polishing apparatus for polishing a bevel portion of a substrate.

2. Description of the Related Art

From a viewpoint of improving a yield in semiconductor fabrications, management of a surface condition in a periphery of a wafer has recently been drawing attention. In semiconductor fabrication processes, a number of materials are deposited on a wafer repeatedly to form a multilayer structure. As a result, unwanted films and roughened surface are formed on a periphery which is not used for products. In recent years, it has become more common to transport the wafer by holding only the periphery of the wafer with arms. Under such circumstances, the unwanted films can come off the periphery onto devices formed on the wafer during various processes, resulting in a lowered yield. Thus, it has been customary to polish the periphery of the wafer using a polishing apparatus to remove the unwanted films and the roughened surface.

A polishing apparatus using a polishing tape for polishing a periphery of a substrate (a bare wafer having a film formed thereon) has been known as such a type of polishing apparatus. This type of polishing apparatus polishes the periphery of the substrate by bringing a polishing layer of the polishing tape into sliding contact with the periphery of the substrate. The polishing layer of the polishing tape is formed by abrasive grains and a binder (e.g., resin) that binds the abrasive grains. Diamond abrasive grains are typically used as the abrasive grains. Recently, a polishing apparatus having multiple polishing tapes is used in order to improve a throughput.

An object to be removed by polishing is a multilayer structure constituted by a metal film, an oxide film, and the like. Since the diamond abrasive grains are hard, the polishing tape using the diamond abrasives particles can polish (i.e., remove) various kinds of films constituting such a multilayer structure at a high removal rate. However, polishing using the hard abrasive grains is likely to leave fine scratches on the surface of the wafer, and such scratches can have an adverse influence on subsequent fabrication processes. Furthermore, the diamond abrasive grains are expensive and therefore polishing of the periphery of the substrate using the diamond abrasive grains is an expensive process.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a polishing apparatus and a polishing method capable of realizing a low-cost polishing process of providing a smooth polished surface.

In order to achieve the above object, according to one aspect of the present invention, there is provided a polishing apparatus for polishing a periphery of a substrate. The polishing apparatus includes: a substrate holder configured to rotate the substrate; a first polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a first polishing tool into contact with the periphery of the substrate when rotated by the substrate holder; and a second polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a second polishing tool into contact with the periphery of the substrate when rotated by the substrate holder. The polishing layer of the first polishing tool has hard first abrasive grains, and the polishing layer of the second polishing tool has second abrasive grains that are softer than the first abrasive grains.

In a preferred aspect of the present invention, at least one of the polishing layer of the first polishing tool and the polishing layer of the second polishing tool has the first abrasive grains and the second abrasive grains.

In a preferred aspect of the present invention, the first abrasive grains are diamond abrasive grains; and the second abrasive grains are one of cerium oxide abrasive grains and silica abrasive grains.

In a preferred aspect of the present invention, the polishing apparatus further includes a third polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a third polishing tool into contact with the periphery of the substrate when rotated by the substrate holder. The second abrasive grains are cerium oxide abrasive grains, and the polishing layer of the third polishing tool has silica abrasive grains.

Another aspect of the present invention is to provide a polishing method for polishing a periphery of a substrate. The polishing method includes: rotating the substrate; a first polishing process of polishing the periphery of the substrate by bringing a polishing layer of a first polishing tool into contact with the periphery of the rotating substrate, the polishing layer of the first polishing tool having hard first abrasive grains; and a second polishing process of polishing the periphery of the substrate by bringing a polishing layer of a second polishing tool into contact with the periphery of the rotating substrate, the polishing layer of the second polishing tool having second abrasive grains that are softer than the first abrasive grains.

According to the present invention, a smooth polished surface with no scratches can be formed as a result of using the second abrasive grains that are softer than the hard first abrasive grains. Further, in a case of using the diamond abrasive grains as the first abrasive grains, use of the cerium oxide abrasive grains or the silica abrasive grains as the second abrasive grains can reduce an amount of the diamond abrasive grains to be used. Therefore, a low-cost polishing process can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing a periphery of a substrate;

FIG. 2 is a plan view showing a polishing apparatus according to an embodiment of the present invention;

FIG. 3 is a vertical cross-sectional view of the polishing apparatus shown in FIG. 2;

FIG. 4 is an enlarged view of a polishing head;

FIG. 5 is a plan view showing an example in which various types of polishing tapes are set in the polishing apparatus;

FIG. 6 is a plan view showing another example in which various types of polishing tapes are set in the polishing apparatus;

FIG. 7 is a plan view showing still another example in which various types of polishing tapes are set in the polishing apparatus;

FIG. 8 is a plan view showing an example in which polishing tapes each having mixed abrasive grains are set in the polishing apparatus;

FIG. 9 is a plan view showing another example in which polishing tapes each having mixed abrasive grains are set in the polishing apparatus;

FIG. 10 is a plan view showing an example in which various types of polishing tapes are set in two polishing apparatuses;

FIG. 11 is a plan view showing an example in which various types of polishing tapes are set in four polishing apparatuses;

FIG. 12 is a view showing cross sections each illustrating part of a substrate having a bare wafer, a SiN film formed on the bare wafer, an oxide film formed on the SiN film, and a protection film formed on the oxide film;

FIG. 13 is a view showing cross sections each illustrating part of a substrate having a bare wafer, an oxide film formed on the bare wafer, a SiN film formed on the oxide film, and a protection film formed on the SiN film;

FIG. 14 is a view showing procedures of polishing a multilayer structure until a surface of a bare wafer is exposed; and

FIG. 15 is a view showing procedures of polishing the multilayer structure using diamond abrasive grains, cerium oxide abrasive grains, and silica abrasive grains.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings.

In this specification, a periphery of a substrate is defined as a region including a bevel portion and near-edge portions. FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing a periphery of a substrate. More specifically, FIG. 1A shows a cross-sectional view of a so-called straight-type substrate, and FIG. 1B shows a so-called round-type substrate.

In the substrate W shown in FIG. 1A, the bevel portion is a portion B that is constituted by an upper slope (an upper bevel portion) P, a lower slope (a lower bevel portion) Q, and a side portion (an apex) R, all of which are located in a circumferential surface of the substrate W. In the substrate W shown in FIG. 1B, a bevel portion is a portion B having a curved cross section with a certain curvature and located in a circumferential surface of the substrate W. The near-edge portions are regions located radially inwardly of the bevel portion B and are indicated by flat sections E1 and E2 located radially outwardly of a region D where devices are formed.

FIG. 2 is a plan view showing a polishing apparatus according to an embodiment of the present invention. FIG. 3 is a vertical cross-sectional view of the polishing apparatus shown in FIG. 2. The polishing apparatus according to this embodiment is structured as a polishing module. As will be described later, multiple polishing modules may be combined to form a single polishing apparatus.

As shown in FIG. 2 and FIG. 3, the polishing apparatus includes a rotary holding mechanism (i.e., a substrate holder) 3 configured to hold a substrate W (i.e., a workpiece to be polished) horizontally and rotate the substrate W. The rotary holding mechanism 3 is located in the center of the polishing apparatus. FIG. 2 shows a state in which the rotary holding mechanism 3 holds the substrate W. This rotary holding mechanism 3 has a dish-shaped holding stage 4 configured to hold a rear surface of the substrate W by a vacuum suction, a hollow shaft 5 coupled to a central portion of the holding stage 4, and a motor M1 for rotating the hollow shaft 5. The substrate W is placed onto the holding stage 4 by hands of a transport mechanism (not shown in the drawing) such that a center of the substrate W is aligned with a rotational axis of the hollow shaft 5.

The hollow shaft 5 is supported by ball spline bearings (linear motion bearings) 6 which are configured to allow the hollow shaft 5 to move vertically. The holding stage 4 has an upper surface having grooves 4 a. These grooves 4 a are connected to a communication passage 7 extending through the hollow shaft 5. The communication passage 7 is coupled to a vacuum line 9 via a rotary joint 8 which is provided on a lower end of the hollow shaft 5. The communication passage 7 is also coupled to a nitrogen-gas supply line 10 for use in releasing a processed substrate W from the holding stage 4. By selectively coupling the vacuum line 9 and the nitrogen-gas supply line 10 to the communication passage 7, the substrate W is attracted to the upper surface of the holding stage 4 by the vacuum suction and released from the upper surface of the holding stage 4.

The hollow shaft 5 is rotated by the motor M1 via a pulley p1 coupled to the hollow shaft 5, a pulley p2 secured to a rotational shaft of the motor M1, and a belt b1 riding on these pulleys p1 and p2. The rotational shaft of the motor M1 extends parallel to the hollow shaft 5. With these structures, the substrate W, held on the upper surface of the holding stage 4, is rotated by the motor M1.

The ball spline bearing 6 is a bearing that allows the hollow shaft 5 to move freely in its longitudinal direction. The ball spline bearings 6 are mounted on a casing 12. Therefore, in this embodiment, the hollow shaft 5 is allowed to move linearly up and down relative to the casing 12, and the hollow shaft 5 and the casing 12 can rotate in unison. The hollow shaft 5 is coupled to an air cylinder (elevating mechanism) 15, so that the hollow shaft 5 and the holding stage 4 can be elevated and lowered by the air cylinder 15.

A casing 14 is provided so as to surround the casing 12. The casing 12 and the casing 14 are in a concentric arrangement. Radial bearings 18 are provided between the casing 12 and the casing 14, so that the casing 12 is rotatably supported by the radial bearings 18. With these structures, the rotary holding mechanism 3 can rotate the substrate W about its central axis Cr and can elevate and lower the substrate W along the central axis Cr.

As shown in FIG. 2, four polishing head assemblies (polishing sections) 1A, 1B, 1C, and 1D are arranged around the substrate W held by the rotary holding mechanism 3. Tape supplying and recovering mechanisms 2A, 2B, 2C, and 2D are provided radially outwardly of the polishing head assemblies 1A, 1B, 1C, and 1D, respectively. The polishing head assemblies 1A, 1B, 1C, and 1D are isolated from the tape supplying and recovering mechanisms 2A, 2B, 2C, and 2D by a partition 20. An interior space of the partition 20 provides a polishing room 21. The four polishing head assemblies 1A, 1B, 1C, and 1D and the holding stage 4 are located in the polishing room 21. On the other hand, the tape supplying and recovering mechanisms 2A, 2B, 2C, and 2D are located outside the partition 20 (i.e., outside the polishing room 21). The respective polishing head assemblies 1A, 1B, 1C, and 1D have the same structure, and the respective tape supplying and recovering mechanisms 2A, 2B, 2C, and 2D have the same structure. Thus, the polishing head assembly 1A and the tape supplying and recovering mechanism 2A will be described in detail below.

The tape supplying and recovering mechanism 2A includes a supply reel 24 for supplying a polishing tape (i.e., a polishing tool) 23 to the polishing head assembly 1A, and a recovery reel 25 for recovering the polishing tape 23 that has been used in polishing of the substrate W. The supply reel 24 is arranged above the recovery reel 25. Motors M2 are coupled respectively to the supply reel 24 and the recovery reel 25 via couplings 27 (FIG. 2 shows only the coupling 27 and the motor M2 coupled to the supply reel 24). Each of the motors M2 is configured to exert a constant torque in a predetermined rotational direction so as to apply a predetermined tension to the polishing tape 23.

The polishing tape 23 is a long tape-shaped polishing tool, and one of surfaces thereof provides a polishing surface. The polishing tape 23 is wound on the supply reel 24, which is mounted on the tape supplying and recovering mechanism 2A. Both sides of the wound polishing tape 23 are supported by reel plates so as not to collapse. One end of the polishing tape 23 is attached to the recovery reel 25, so that the recovery reel 25 takes up the polishing tape 23 supplied to the polishing head assembly 1A to thereby recover the polishing tape 23. The polishing head assembly 1A has a polishing head 30 for pressing the polishing tape 23, supplied from the tape supplying and recovering mechanism 2A, against a periphery of the substrate W The polishing tape 23 is supplied to the polishing head 30 such that the polishing surface of the polishing tape 23 faces the substrate W

The tape supplying and recovering mechanism 2A has plural guide rollers 31, 32, 33, and 34. The polishing tape 23, to be supplied to and recovered from the polishing head assembly 1A, is guided by these guide rollers 31, 32, 33, and 34. The polishing tape 23 is supplied to the polishing head 30 from the supply reel 24 through an opening 20 a formed in the partition 20, and the used polishing tape 23 is recovered by the recovery reel 25 through the opening 20 a.

As shown in FIG. 3, an upper supply nozzle 36 is provided above the substrate W. This upper supply nozzle 36 is to supply a polishing liquid onto a center of an upper surface of the substrate W held by the rotary holding mechanism 3. Lower supply nozzles 37 are provided for supplying a polishing liquid onto a boundary between the rear surface of the substrate W and the holding stage 4 of the rotary holding mechanism 3 (i.e., onto a periphery of the holding stage 4). Typically, pure water is used as the polishing liquid. Alternatively, ammonia may be used in a case where silica is used as abrasive grains of the polishing tape 23.

The polishing apparatus further includes cleaning nozzles 38 each for cleaning the polishing head 30 after the polishing process. Each of the cleaning nozzles 38 ejects cleaning water toward the polishing head 30 after the substrate W is elevated by the rotary holding mechanism 3 to thereby clean the polishing head 30 used in the polishing process.

In order to isolate the ball spline bearings 6 and the radial bearings 18 from the polishing room 21 when the hollow shaft 5 is elevated and lowered relative to the casing 12, the hollow shaft 5 and an upper end of the casing 12 are coupled to each other by a bellows 19 that is extendible and contractible in a vertical direction, as shown in FIG. 3. FIG. 3 shows a state in which the hollow shaft 5 is in a lowered position and the holding stage 4 is in a polishing position. After the polishing process, the air cylinder 15 elevates the substrate W, together with the holding stage 4 and the hollow shaft 5, to a transport position, where the substrate W is released from the holding stage 4.

The partition 20 has an entrance 20 b through which the substrate W is transported into and removed from the polishing room 21. The entrance 20 b is in a shape of horizontally extending notch. Therefore, the substrate W, held by the transport mechanism, can travel horizontally across the polishing room 21 through the entrance 20 b. An upper surface of the partition 20 has an opening 20 c and louvers 40, and a lower surface of the partition 20 has a gas-discharge opening (not shown in the drawing). During the polishing process, the entrance 20 b is closed by a non-illustrated shutter. Therefore, when a fan mechanism (not shown in the drawing) is driven to evacuate a gas in the polishing room 21, downward flow of a clean air is formed in the polishing room 21. Because the polishing process is performed under such conditions, the polishing liquid is prevented from scattering upwardly. Therefore, the polishing process can be performed while keeping an upper space of the polishing room 21 clean.

FIG. 4 is an enlarged view of the polishing head 30. As shown in FIG. 4, the polishing head 30 has a press mechanism 41 configured to apply pressure to a rear surface of the polishing tape 23 to press the polishing surface of the polishing tape 23 against the substrate W at a predetermined force. The polishing head 30 further includes a tape-sending mechanism 42 configured to send the polishing tape 23 from the supply reel 24 to the recovery reel 25. The polishing head 30 has plural guide rollers 43, 44, 45, 46, 47, 48, and 49, which guide the polishing tape 23 such that the polishing tape 23 travels in a direction perpendicular to a tangential direction of the substrate W.

The tape-sending mechanism 42 of the polishing head 30 includes a tape-sending roller 42 a, a tape-holding roller 42 b, and a motor M3 configured to rotate the tape-sending roller 42 a. The motor M3 is mounted on a side surface of the polishing head 30. The tape-sending roller 42 a is coupled to a rotational shaft of the motor M3. The polishing tape 23 is wound about half around the tape-sending roller 42 a. The tape-holding roller 42 b is located next to the tape-sending roller 42 a. The tape-holding roller 42 b is supported by a non-illustrated mechanism, which exerts a force on the tape-holding roller 42 b in a direction indicated by NF in FIG. 4 (i.e., in a direction toward the tape-sending roller 42 a) so as to press the tape-holding roller 42 b against the tape-sending roller 42 a.

As the motor M3 rotates in a direction indicated by arrow in FIG. 4, the tape-sending roller 42 a rotates to send the polishing tape 23 from the supply reel 24 to the recovery reel 25 via the polishing head 30. The tape-holding roller 42 b is configured to be rotatable freely about its own axis and is rotated as the polishing tape 23 is sent by the tape-sending roller 42 a.

The press mechanism 41 includes a press pad 50 located at the rear side of the polishing tape 23 and an air cylinder (an actuator) 52 configured to move the press pad 50 toward the substrate W. The air cylinder 52 is a so-called single rod cylinder. A load of the press pad 50 that presses the polishing tape 23 against the substrate W is controlled by air pressure supplied to the air cylinder 52.

As shown in FIG. 2, the polishing head 30 is secured to one end of an arm 60, which is rotatable about an axis Ct extending parallel to the tangential direction of the substrate W. The other end of the arm 60 is coupled to a motor M4 via pulleys p3 and p4 and a belt b2. As the motor M4 rotates in a clockwise direction and a counterclockwise direction through a certain angle, the arm 60 rotates about the axis Ct through a certain angle. In this embodiment, the motor M4, the arm 60, the pulleys p3 and p4, and the belt b2 constitute a tilting mechanism for tilting the polishing head 30. The tilting motion of the polishing head 30 is performed before polishing or during polishing. This tilting motion of the polishing head 30 enables the polishing tape 23 to polish not only the bevel portion but also the near-edge portions of the substrate W.

As shown in FIG. 3, the tilting mechanism is mounted on a movable base 61 in a plate shape. This movable base 61 is movably coupled to a base plate 65 via guides 62 and rails 63. The rails 63 extend linearly along a radial direction of the substrate W held on the rotary holding mechanism 3, so that the movable base 61 can move linearly along the radial direction of the substrate W. A connection plate 66, extending through the base plate 65, is secured to the movable base 61. A linear actuator 67 is coupled to the connection plate 66 via a joint 68. This linear actuator 67 is secured to the base plate 65 directly or indirectly.

The linear actuator 67 may comprise an air cylinder or a combination of a positioning motor and a ball screw. The linear actuator 67, the rails 63, and the guides 62 constitute a moving mechanism for linearly moving the polishing head 30 along the radial direction of the substrate W. Specifically, the moving mechanism is operable to move the polishing head 30 along the rails 63 closer to and away from the substrate W. On the other hand, the tape supplying and recovering mechanism 2A is fixed to the base plate 65. The tilting mechanisms, the press mechanisms 41, and the tape-sending mechanisms 42 of the four polishing head assemblies 1A, 1B, 1C, and 1D arranged around the substrate W and the moving mechanisms for moving the respective polishing head assemblies are configured to operate independently of each other.

The polishing tape 23 comprises a base tape made from PET sheet or the like and a polishing layer formed on the base tape. The polishing layer comprises a binder (e.g., resin) covering one surface of the base tape and abrasive grains bound by the binder. A surface of the polishing layer provides the polishing surface. The abrasive grains are selected from diamond abrasive grains, cerium oxide abrasive grains, silica abrasive grains, mixed abrasive grains composed of the diamond abrasive grains and the cerium oxide abrasive grains, and mixed abrasive grains composed of the diamond abrasive grains and the silica abrasive grains. The diamond abrasive grains serve as hard first abrasive grains, and the cerium oxide abrasive grains and the silica abrasive grains serve as second abrasive grains that are softer than the first abrasive grains. Hereinafter, a polishing tape using the diamond abrasive grains will be referred to as a polishing tape 23A, a polishing tape using the cerium oxide abrasive grains will be referred to as a polishing tape 23B, a polishing tape using the silica abrasive grains will be referred to as a polishing tape 23C, a polishing tape using the mixed abrasive grains composed of the diamond abrasive grains and the cerium oxide abrasive grains will be referred to as a polishing tape 23D, and a polishing tape using the mixed abrasive grains composed of the diamond abrasive grains and the silica abrasive grains will be referred to as a polishing tape 23E.

FIG. 5 is a plan view showing an example in which various types of polishing tapes are set in the above-described polishing apparatus. In FIG. 5, the polishing tapes 23B using the cerium oxide abrasive grains are mounted on the polishing head assemblies 1A and 1C, and the polishing tapes 23A using the diamond abrasive grains are mounted on the polishing head assemblies 1B and 1D. In this case, instead of the polishing tapes 23B, the polishing tapes 23C using the silica abrasive grains may be mounted on the polishing head assemblies 1A and 1C.

FIG. 6 is a plan view showing another example in which various types of polishing tapes are set in the above-described polishing apparatus. In FIG. 6, the polishing tapes 23B using the cerium oxide abrasive grains are mounted on the polishing head assemblies 1A, 1B, and 1C, and the polishing tape 23A using the diamond abrasive grains is mounted on the polishing head assembly 1D. In this case also, instead of the polishing tapes 23B, the polishing tapes 23C using the silica abrasive grains may be mounted on the polishing head assemblies 1A, 1B, and 1C.

FIG. 7 is a plan view showing still another example in which various types of polishing tapes are set in the above-described polishing apparatus. In FIG. 7, the polishing tape 23B using the cerium oxide abrasive grains is mounted on the polishing head assembly 1A, the polishing tapes 23A using the diamond abrasive grains are mounted on the polishing head assemblies 1B and 1D, and the polishing tape 23C using the silica abrasive grains is mounted on the polishing head assembly 1C.

FIG. 8 and FIG. 9 are plan views each showing still another example in which the polishing tapes having the mixed abrasive grains are set in the above-described polishing apparatus. In FIG. 8, the polishing tapes 23D using the mixed abrasive grains composed of the diamond abrasive grains and the cerium oxide abrasive grains are mounted on the polishing head assemblies 1A, 1B, 1C, and 1D. In FIG. 9, the polishing tapes 23E using the mixed abrasive grains composed of the diamond abrasive grains and the silica abrasive grains are mounted on the polishing head assemblies 1A, 1B, 1C, and 1D.

FIG. 10 is a plan view showing still another example in which various types of polishing tapes are set in two polishing apparatuses. A first polishing apparatus 100 and a second polishing apparatus 200 have the same structure as that of the above-described polishing apparatus. A combination of the first polishing apparatus (i.e., first polishing module) 100 and the second polishing apparatus (i.e., second polishing module) 200 constitutes a single polishing apparatus. The first polishing apparatus 100 has polishing head assemblies 1A, 1B, 1C, and 1D, and the second polishing apparatus 200 has polishing head assemblies 1E, 1F, 1G and 1H. The polishing tapes 23A using the diamond abrasive grains are set in the first polishing apparatus 100, and the polishing tapes 23B using the cerium oxide abrasive grains are set in the second polishing apparatus 200. In this case, instead of the polishing tapes 23B, the polishing tapes 23C using the silica abrasive grains may be set in the polishing apparatus 200. In the example shown in FIG. 10, the substrate W is first polished in the first polishing apparatus 100, and then polished in the second polishing apparatus 200.

FIG. 11 is a plan view showing still another example in which various types of polishing tapes are set in four polishing apparatuses. The first polishing apparatus 100, the second polishing apparatus 200, a third polishing apparatus 300, and a fourth polishing apparatus 400 have the same structure as that of the above-described polishing apparatus. A combination of the first to fourth polishing apparatuses (i.e., first to fourth polishing modules) 100, 200, 300, and 400 constitutes a single polishing apparatus. The polishing tapes 23A using the diamond abrasive grains are set in the first polishing apparatus 100 and the third polishing apparatus 300, the polishing tapes 23B using the cerium oxide abrasive grains are set in the second polishing apparatus 200, and the polishing tapes 23C using the silica abrasive grains are set in the fourth polishing apparatus 400. In this example, the substrate W is polished in the order of the first polishing apparatus 100, the second polishing apparatus 200, the third polishing apparatus 300, and the fourth polishing apparatus 400.

While each polishing apparatus (polishing module) has the four polishing head assemblies in this embodiment, the present invention is not limited to this configuration. For example, two, three, or more than four polishing head assemblies may be provided in each polishing apparatus (polishing module).

Next, application examples using the above-described polishing apparatus will be described.

Application Example 1

When polishing a multilayer structure comprising a relatively soft oxide film (e.g., thermal oxide film, TEOS film, SiO₂ film) and a hard film (e.g., SiN film, metal film, protection film), the cerium oxide abrasive grains (the polishing tape 23B) or the silica abrasive grains (the polishing tape 23C) are used to polish the oxide film and the diamond abrasive grains (the polishing tape 23A) are used to polish the hard film.

Application Example 2

When the oxide film is formed on the SiN film, this SiN film can function as a polishing stopper, because a polishing rate (i.e., a removal rate) of the SiN film is lower than a polishing rate of the oxide film. An example of this application will be described with reference to FIG. 12. FIG. 12 is a view showing cross sections each illustrating part of a substrate having a bare wafer (typically a silicon wafer) 81, a SiN film 82 formed on the bare wafer 81, an oxide film 83 formed on the SiN film 82, and a protection film 84 formed on the oxide film 83. In this example, the diamond abrasive grains are firstly used to polish (remove) the protection film 84, and then the cerium oxide abrasive grains are used to polish the oxide film 83. Because the SiN film 82, underlying the oxide film 83, is hardly polished by the cerium oxide abrasive grains, the progress of polishing becomes slow when the SiN film 82 is exposed. Therefore, polishing can be stopped when the SiN film 82 is exposed.

Application Example 3

When polishing a multilayer structure or a single film, the diamond abrasive grains may be firstly used to polish it at a high polishing rate for a predetermined period of time or until a polishing end point is detected, and then the cerium oxide abrasive grains or the silica abrasive grains may be used to polish it for a predetermined period of time. By using the cerium oxide abrasive grains or the silica abrasive grains after using the diamond abrasive grains, fine irregularities and scratches on a polished surface can be removed.

Application Example 4

FIG. 13 is a view showing cross sections each illustrating part of a substrate having a bare wafer (typically a silicon wafer) 81, an oxide film 83 formed on the bare wafer 81, a SiN film 82 formed on the oxide film 83, and a protection film 84 formed on the SiN film 82. In this example, the diamond abrasive grains are firstly used to polish (remove) the protection film 84 and the SiN film 82, and then the cerium oxide abrasive grains or the silica abrasive grains are used to polish the oxide film 83 for a predetermined period of time or until a polishing end point is detected.

Application Example 5

FIG. 14 is a view showing procedures of polishing a multilayer structure until a surface of a bare wafer (e.g., a silicon wafer) 81 is exposed. A substrate used in this example has the same structure as that of the substrate shown in FIG. 12. As shown in FIG. 14, first, the diamond abrasive grains are used to remove the multilayer structure in its entirety to expose the surface of the bare wafer 81. Then, the silica abrasive grains are used to finish-polish the surface of the bare wafer 81 to remove fine irregularities on the polished surface.

Application Example 6

The mixed abrasive grains (i.e., the polishing tape 23D or the polishing tape 23E) may be used to polish the multilayer structure in its entirety shown in FIG. 14. For example, in the case of using the mixture of the diamond abrasive grains and the cerium oxide abrasive grains, the oxide film is polished by the diamond abrasive grains and the cerium oxide abrasive grains, and the protection film and the SiN film are polished only by the diamond abrasive grains. In the case of using the mixture of the diamond abrasive grains and the silica abrasive grains, polishing can also be performed in the same manner. Use of such mixed abrasive grains can reduce an amount of the diamond abrasive grains used. When using the above-described mixed abrasive grains, the surface of the bare wafer may be finish-polished using the silica abrasive grains.

Application Example 7

The polishing tape 23A having the diamond abrasive grains and the polishing tape 23B having the cerium oxide abrasive grains (or the polishing tape 23C having the silica abrasive grains) can be simultaneously brought into contact with the periphery of the substrate W so as to polish the periphery. In this case also, the oxide film is polished by the cerium oxide abrasive grains and the diamond abrasive grains, and a hard film, such as the protection film and the SiN film, is polished only by the diamond abrasive grains.

Application Example 8

An application example using the polishing apparatus shown in FIG. 7 and FIG. 11 will be described with reference to FIG. 15. First, the diamond abrasive grains are used to remove the protection film 84. Next, the cerium oxide abrasive grains are used to remove the oxide film 83. Subsequently, the diamond abrasive grains are used to remove the SiN film 82. Then, the silica abrasive grains are used to finish-polish the surface of the bare wafer 81.

As described above, use of the combination of the diamond abrasive grains and the cerium oxide abrasive grains or the silica abrasive grains can provide a polished surface with no scratches. Further, because the amount of the diamond abrasive grains can be reduced, a low-cost polishing process can be realized.

The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims and equivalents. 

1. A polishing apparatus for polishing a periphery of a substrate, said polishing apparatus comprising: a substrate holder configured to rotate the substrate; a first polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a first polishing tool into contact with the periphery of the substrate when rotated by said substrate holder; and a second polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a second polishing tool into contact with the periphery of the substrate when rotated by said substrate holder, wherein said polishing layer of said first polishing tool has hard first abrasive grains, and said polishing layer of said second polishing tool has second abrasive grains that are softer than said first abrasive grains.
 2. The polishing apparatus according to claim 1, wherein at least one of said polishing layer of said first polishing tool and said polishing layer of said second polishing tool has said first abrasive grains and said second abrasive grains.
 3. The polishing apparatus according to claim 1, wherein: said first abrasive grains are diamond abrasive grains; and said second abrasive grains are one of cerium oxide abrasive grains and silica abrasive grains.
 4. The polishing apparatus according to claim 3, further comprising: a third polishing section configured to polish the periphery of the substrate by bringing a polishing layer of a third polishing tool into contact with the periphery of the substrate when rotated by said substrate holder, wherein said second abrasive grains are cerium oxide abrasive grains, and said polishing layer of said third polishing tool has silica abrasive grains.
 5. A polishing method for polishing a periphery of a substrate, said polishing method comprising: rotating the substrate; a first polishing process of polishing the periphery of the substrate by bringing a polishing layer of a first polishing tool into contact with the periphery of the rotating substrate, the polishing layer of the first polishing tool having hard first abrasive grains; and a second polishing process of polishing the periphery of the substrate by bringing a polishing layer of a second polishing tool into contact with the periphery of the rotating substrate, the polishing layer of the second polishing tool having second abrasive grains that are softer than the first abrasive grains.
 6. The polishing method according to claim 5, wherein at least one of the polishing layer of the first polishing tool and the polishing layer of the second polishing tool has the first abrasive grains and the second abrasive grains.
 7. The polishing method according to claim 5, wherein: the first abrasive grains are diamond abrasive grains; and the second abrasive grains are one of cerium oxide abrasive grains and silica abrasive grains.
 8. The polishing method according to claim 7, further comprising: a third polishing process of polishing the periphery of the substrate by bringing a polishing layer of a third polishing tool into contact with the periphery of the rotating substrate, wherein the second abrasive grains are cerium oxide abrasive grains, and the polishing layer of the third polishing tool has silica abrasive grains. 